Electric circuit



Feb. 113-11. y. c. HALL TAL 2,231,653 I ELEc'rRQIc CIRCUIT Filed Jun@- 25. 1938 2 Sheets-Shee- 3.

@I HQI. U Z B: ILI

D. g E I, *I BLACK PRINTER BLUE-GREEN MAGENTA YELLQw SUBTRACTIVE PRIMARIES FIG .3.

RED SIGNAL INPUT GREEN SIGNAL INPUT S To GREEN VINCENT C. `LILL RICHARD $.MORSE Feb. l1, 1941. v. c. HALL Erm.. 2,231,668

1 ELECTRIC CIRQUIT Filed June- 25. 1958 2 Sheets-Sheet 2 F|G.Z. .L

RED CHANNEL VALVl" VALVE 15H u @Mumie I- IOR IIR 12R/l CONTROL GREEN CHANNEL L 16 AMPLIFIER f g l L. BLACK 10G G 12aj coNTRoL CHANNEL BLUE CHANNEL Y [IQIVAMRLIFIER 10B na '12 s); coNTRoL iwan/WOM VINCENT HALL RICHARD S;MORSE Patented Feb. 11, 1941 T STES! PATENT OFFICE ELECTRIC" CIRCUIT Application .lune 25, 1938, Serial No. 215,822

7 Claims.

for use in photo-mechanical processes as de scribed in a copending application Serial Number Y, 138,351, J. A. C. Yule, filed April 22, 1938. Yule discloses a black printer whose printing density at each point is equal to the least predominate subtractive color content of the corresponding point of the original and he describes in detail two methods of making such a printer. 'Ihe present invention when applied to electro-optical color reproducing systems provides a third method of making this highly desirable type of black printer.

Another object of the invention is to provide improved radio reception by minimizingundelsirable factors such as static, fading, etc.

It is a general object of the invention to provide an electric circuit which is responsive to the smallest or largest (i. e. one of the extremes) of a number of independent variables.

According to the invention there is provided an electric circuit comprising a plurality of channels each bearing an electric signaL'for example the signal corresponding to one of the colored constituents of a multi-colored picture which is being reproduced. The circuit also includes a single amplier connected to the output of all of the separate channels, responsive only to the output of the channel in which the intensity of the signal is the greatest or the least of all the signals.

More specifically the invention, when applied to two channels only, consists in having a control connected across the two channels this control comprising an electric circuit having positive output only when the difference in the intensities of the two signals is in a given direction. That is, only when the intensity in the first channel, say, is greater than the intensity in the second channel. There is also provided in one of the channels, a valve, usually an amplifier, which transmits the signal through its channel only when it receives a positive output from the abovementioned control to which it is connected. Thus the final output of the channel having the valve is Zero except when the intensity in the rst channel is, in the sample discussed, greater than the intensity of the signal in the second channel. Furthermore, in the preferred embodiment of the invention the output of the transmitting valve is either zero (when the control is not positive) or has a uniform amplification factor for all positive values of the control output.

In general, the point at which the valve responds to the output of the control is not exactly zero potential. In fact, there is no reason for limiting this threshold value to any one particular potential. The valve may be arranged so that it transmits current only when the input to its control electrode is within a certain range and the control is arranged so that its output is within this certain range only when the difference in the intensities of the two signals is in a given direction. Theoretically, the range of potentials may be any between minus infinity and plus. infinity.

When applying the invention directly to a large number of channels, two controls are connected across each pair of channels and the output of each control is connected to a valve in one of the two channels. If there are N channels, there would be (N-l) valves in each channel and N(N-1) controls. Since the present invention `relates primarily to three channel systems, a relatively simple set-up results, but if agreater number of channels are involved, it probably would be preferable to combine some of the units.

Although this invention is primarily intended Yfor the making of a black printer, it finds many applications in radio reception. For example, when several signal-s bearing the same intelligence (e. g. radio program)` are received simultaneously, the invention may be arranged so that only the strongest signal will be utilized. For example, the separate signals (originating at the adjacent microphones) may be on different wave lengths, they may be coming from diierent broadcasting stations on the same network, or they may be from separate antennae differently arranged with respect to the polarization of the incoming waves. Thus the effects of fading are minimized by selecting the wave length, the station and/or the plane of polarization which has faded least.

The invention, its objects and its advantages will be fully understood from the following description when read in connection with the accompanying drawings, in which:

Fig. `1 illustrates the properties of a black printer made according to the invention.

Fig.. 2 shows an electric circuit incorporating the invention and Fig. 3 illustrates in. detail a portion of the circuit shownl in Fig. 2.

Fig. 1 graphically illustrates the relative percentages of the three subtractive primary colors of one point on a multi-colored scene or picture. These relative percentages correspond to the percentages of the pigments, inks, or dyes used in reproducing the multi-colored original. A black printer is desired whose printing density at any point is some function of the least predominant 4subtractive color component at that point. In the example shown, a black printer would be made up having a printing density oorresponding to the density of the magenta and the other color printers would have printing densities proportional to the difference between their predominance and the predominance of the magenta. That is, the magenta printer would have zero or practically Zero printing density at this particular point and the yellow and bluegreen printers would have a printing density proportional to the difference in heights of the corresponding blocks in the figures.

By way of definition of the terms and phrases used in this specification, it is pointed out that the primary colors or primaries are red, greenand blue and that the colors complementary to these namely, minus red, minus green and minus blue are called the subtractive primaries and are respectively blue-green, magenta and yellow. Any point on any object has a color which may be thought of as being made up of the three primary colors or of the three subtractive primaries. The relative proportions of the primary colors are inverse to the respective relative proportions of the subtractive primaries. Thus, a point which reflects green more than blue or red is predominantly green and hence is made up of large amounts of yellow and blue-green pigments but very little magenta. The least predominant subtractive color content of that point is magenta.

The reproduction of that point photomechanically requires relatively large amounts of yellow and blue-green inks but very little magenta. As pointed out, a black printer should in this case have a primary density corresponding to this latter magenta content which is, of course, proportional to the magenta content of the original point (the least predominant subtractive color content of the original point) and which in turn -is inversely proportional tothe predominant primary color content of the original point (color correction being taken into account if applied).

In Fig. 2 the respective color channels are labeled according to the color of the original scanning beams, i e. according to the primary colors. The outputs of the red, green, and blue channels control .the printing density of the bluegreen, magenta, and'yellow printers respectively. According to the present invention a portion of the output of each of these channels is combined in the circuit shown, to produce a black printer whose printing density at any point corresponds in an inverse manner to the intensity of the most predominant primary color, i. e., directly to the intensity of the least predominant subtractive primary color of the original.

Although the present invention is concerned primarily with the making of a black printer, it should be pointed out that the printing densities of the other printers to be used therewith should be reduced by the printing density of the black printer.

yIn the drawings color filters IDR, IDG and IIIB lter the light reaching photoelectric cells IIR, I IG and I IB which through accompanying ampliners |2R, IZG and I2B control three color electrooptical systems for making color printers in any well-known way, not shown. According to the present invention a portion of the output of each of these amplifiers is fed through channels including valves ISR, 14R, ISG, ILIG, and ISB, MB respectively. The output of all of these channels though suitable transformers is fed into a single black channel indicated by a block I6. According to the invention, these three channels are so arranged that current is transmitted to the corresponding transformer IER, ISG, or IEB in the circuit having the signal Whose intensity is one of the extremes i. e. maximum or minimum. To provide this result, controls 2|, 22, and 23 are connected across each pair of amplifiers IZR, IZG, and IZB, which controls are so arranged that Vthey provide output potentials within certain given ranges only When the difference in intensity of the corresponding pair of signals is in a given direction. By way of example, assuming output of the control 2| leading to a control electrode 2|lG in the valve MG is so arranged that no signal is transmitted through this valve. Similarly the control 23 is arranged so that current will pass through the valve MR but so that no signal will pass through the valve IAB. Since no signal can reach the transformers |5G and 15B, the outputs of the control 22 are not of interest in this example. Thus the black channel I6 responds only to the output of the transformer |5R. The transformers IER etc. may be arranged in series as shown or in parallel.

In order that the output of the transformer |5R will be proportional only to the signal from the amplier |2R and independent of the potentials on the control 'electrodes I8R and 2DR, i. e. proportional only to the potentials on control electrodes I'IR and ISR in the valves |3R and |4R respectively, the characteristics, i. e. the electrode potentials in these valves I3R and I4R are so arranged that the valves (in the green and blue channels as well as in the red channels) transmit no signal except when the control electrodes ISR and ZUR, etc. are within a certain range and have uniform amplification factors independent of the potential on these control electrodes when said potentials are Within the respective ranges. That is, the output of the valve |3R is proportional only to the input on the electrode IIR and independent of the potential on the electrode IBR except for the on and off action. Slight departures from this theoretically perfect set up may be tolerated, but it is desirable to select the tetrode, pentode, etc. which will have properties as near as possible to the ideal when appropriate voltage are applied.

The manner in which the controls 2|, 22, and 23 may be arranged to give these desired effects is more clearly shown in Fig. 3 which is a detailed View of control 2 I. The inputs of the red and green channels are fed into transformers 25 and 26 out of phase as indicated by the cross circuit in the green signal input. The output of .these transformers 25 and 26 is used to control the difference in potential'between the cathode 30 and a control grid 3| in an electron discharge device 29. The cathode is connected to a potentiometer circuit 28 and a rectifier 2l across the transformer 26. By suitably arranging the potentials on the electrodes of the electron discharge device 29, shown as a triode with a screen grid added, the output on the plate 32 is zero or less than some given value for all potentials on the grid 3i provided by input signals in which the intensity of the green signal is greater than the intensity of the red signal. The output of the plate 32 is greater than this given threshold value for grid potentials produced when the red signal intensity is greater than the green. This output is directed through a suitable circuit 33 t0 control a valve ISR as shown in Fig. 2.

A similar but oppositely arranged circuit including transformers 34 and 35, an electron discharge device 36 and a lead 31 permits passage of current through the green channel at the valve MB only when the intensity of the green signal is greater than that of the red signal. W'hen the intensities of two signals are practically equal the controls act to transmit either but not both signals to the output.

Various electron discharge devices having the above characteristics are Well known and some particulariy suitable for this purpose are available on the market. Furthermore, it is also well known that practically any triode can be arranged to give a response within a given range capable of use on a control electrode of a valve and hence almost any triode is more or less satisfactory for a control. It is usually preferred to use a tetrode or a more complex type of valve with the on and off elfect and it is desirable to employ as valves tetrodes whose responses are almost independent of the input to one of the control electrodes, when the voltage on this control electrode is within a certain range. However it is possible to use triodes but this is less preferable since more complex circuits are required.

The following is a detailed outline of a satisfactory circuit. In Fig. 2 the valves |3R, MR, etc., are of the type commercially known as 6L7 (see Radio Corporation of America Manual) which for the purpose of the present invention may be assumed to have a constant amplification of about 500 micro-mhos. The transformer connecting the plate of the first tube (e. g. I3R) to the grid of the second tube e. g. ISR) has a primary impedance of the order of 150,000 ohms, and a step-down voltage ratio of approximately 75 in order to make the input of the second stage equal to that of the first tube or, in other words, to nullify the amplification of this stage. The bias voltage on the grids ISR, 2DR, etc., will vary from approximately -20 volts at equilibrium (no signal) to approximately -3 volts for a signal from the rectier stage.

The output transformers I5R, etc., have a resistance of approximately 150,000 ohms primary and 200 ohms secondary operating into the black channel which preferably has a bridging type transformer input of approximately 10,000 ohms impedance. We have found it desirable to place a 200 ohm resistor across the output terminal of each of the transformers I5R, etc., in order to have this correct balance of impedance.

In Fig. 3 the valves 29 and 35 are of the type commercially known as 6J7. The input to these valves is obtained through a standard coupling transformer (e. g. 25) to the grid of the valve as shown; the transformer 25 having a primary impedance of 500 ohms and a secondary impedance of 200,000 ohms. If the transformer 25 is of the direct interstage type operating from the output of the last tube in the red channel, the primary would have to be about 20,000 ohms and the secondary about 200,000 ohms. The trans- 5 formers 26 and 35, controlling the valve cathodes are identical to the transformers 25 and 3ft. The rectiiiers shown by the conventional symbol (e. g. 21) are the copper oxide type rectier which together with the potentiometers (e. g. 28) show a 10 resistance of approximately 500,000 ohms. The output transformer of valves 2S and 36 each have a primary impedance of approximately 200,000 ohms and a secondary impedance of 100,000 ohms. The rectiers connected to these secondaries are i5 also of the copper oxide (meter) type and the potentiometers 33 and 3l have a resistance of 100,000 ohms each.

Having thus described our invention, we wish to point out that it is not to be limited to the specic examples described but is of the scope ofthe appended claims.

What we claim and desire to secure by Letters Patent of the United States is:

l. An electric circuit for use in making a black 25 printer for photomechanical color reproduction comprising a plurality of available channels each bearing a signal corresponding to one of the color printers to be used along with said black printer, an amplifier connected to the output of all the channels and means responsive to the intensities of the signals for rendering conductive into the amplifier only the channel carrying the signal whose relative intensity is one of the extremes, greatest and least.

2. An electric circuit for use in making a black printer for photomcchanical color reproduction comprising a plurality of channels each bearing a signal corresponding to one of the color printers to be used along with said black printer, a single output circuit connected to the output of all the channels and means responsive to the directions of the differences of the intensities of each pair of signals for rendering conductive into the single output circuit only the channel carrying the signal whose relative intensity is one of the extremes, greatest and least.

3. An electric circuit for use in making a black printer for photomechanical color reproduction comprising a plurality of channels each carrying a signal corresponding to one of the color printers to be used along with said black printer, potential producing means across each two channels and having two output leads with the output on one of the leads within a certain range of potentials only when the difference of intensities of the two channels is in one direction and the output on the other lead within a certain range of potentials only when this dilference is in the other direction, and valves in each of the two channels and connected to said leads for transmitting the signal through the respective channel only when the potential on the respective lead is within the said range for that lead, all oil the valves being similarly connected to operate similarly when the 65 direction of the controlling difference is considered with respect tothe channel containing the valve.

4. An electric circuit for use in making a black printer for photomechanical color reproduction comprising a plurality of channels for carrying independent signals each corresponding to one of the color printers to be used along with said black printer, each channel including valves each of which has in addition to its input and output electrodes a control input electrode and has zero output for zero and negative inputs through the control electrode and substantially uniform positive amplification for positive inputs through this electrode, an electron discharge device connected to each pair of channels to respond positively only when the diierence between the intensities of the signals in the two channels is in one direction when considered with respect to one of the two channels, a second electron discharge device connected across the same two channels to respond positively only when said dilerence is in the same direction when considered with respect to the other of the two channels, means connecting the outputs of the two electron discharge devices respectively to the control electrodes of valves in each of the two channels, all of the electron discharge devices operating in the same direction when considered with respect to the channels containing the valvespto which they are respectively connected, whereby the signal in any 4one channel will be transmitted by all of its valves an electric signal corresponding to each color,

only when said intensity difference relative to each of the other channels is in said direction with respect to said one channel.

5. An electro optical system for making a black printer for use in the photomechanical reproduction of a multicolored original comprising means for scanning the original in a plurality of colors and for establishing in separate channels scanning means for synchronously recording a -black separation image, means in each channel responsive to the signal intensities for transmitting the signal therethrough only when said signals intensity is greater than that of any of the other signals and means connected to the output of all the channels for controlling the energy of the recording scanning means whereby each point of the black separation image will have an intensity in accordance with the intensity of the signal which is greatest at that point.

6. A electro-optical circuit comprising three channels respectively bearing signals corresponding to the primary colors, a fourth channel connected to the output of each of the three channels and means responsive to the intensities of the signals for rendering conductive into the fourth channel only the channel carrying the signal whose relative intensity is the greatest of the three.

7. An electro optical circuit comprising a plurality of available channels each bearing a signal corresponding to a color component, an amplifier connected to the output of all the channels and means responsive to the intensities of the signals for rendering non-conductive to the amplier all of the channels except one, said all of the chan- 25 VINCENT C. HALL. RICHARD S. MORSE. 

